The present invention relates to the field of hydrocarbon upgrading processes. In another aspect, the invention relates to the desulfurization of cracked gasoline.
Hydrodesulfurization is a process primarily intended to convert the organic sulfur compounds contained in a hydrocarbon feedstream to hydrogen sulfide which is subsequently removed from the hydrocarbon feedstream.
When a petroleum fraction charged to a cracker contains sulfur, the resulting cracked gasoline also contains sulfur. The sulfur concentration in gasoline must be extremely low in order to meet environmental standards. In fact, debate is ongoing as to whether the sulfur level in gasoline should be further reduced. Thus, it is desirable to reduce the level of sulfur in gasoline to the extent possible.
In addition to meeting environmental standards for sulfur content, gasoline boiling range material, for example, naphtha, is often desulfurized prior to upgrading in an aromatization process due to concerns that the presence of sulfur will have an adverse impact on either the aromatization process or on the aromatization catalyst, or both. However, hydrodesulfurization of organic sulfur compounds contained in cracked gasoline is expected, by those skilled in the art, to result in the saturation of the unsaturated hydrocarbons, such as olefins, contained in the cracked gasoline. This is undesirable because of the resulting reduction in total octane of the cracked gasoline and because of the substantial consumption of hydrogen in saturating the olefins.
Total octane, as used herein, is defined as the flow rate, in liters/hour, of a hydrocarbon stream multiplied by the research octane number (RON) of the hydrocarbon stream. RON, as used herein, refers to the octane number of a hydrocarbon stream as determined using the ASTM D-2722 method.
Subsequent treatment of the cracked gasoline would then be required in order to recover the loss in total octane resulting from the hydrodesulfurization. Therefore, development of a process for desulfurizing cracked gasoline wherein the total octane is not reduced by the hydrodesulfurization would be a significant contribution to the art.